God Bless The US - It's an S with a U superimposed on it (US - duh). Over time, the bar underneath the U disappeared, leaving two parallel lines || running through the S.

The Peso Theory - A similar theory involves a symobol devised to represent pesos. "The dollar sign was invented by Oliver Pollock, an Irish immigrant who settled in Carlisle, Pennsylvania, in the 18th century, setting himself up as a West Indies trader. He later moved to Louisiana, where his success enabled him to supply the Patriots’ cause in the Revolutionary War, via trade with the local Spaniards, and using the peso as a trading currency. In his accounts, Pollock used an abbreviated sign for pesos, consisting of the letters 'p' and 's' superimposed - looking like the modern dollar sign. In 1775, the US Congress decided to revamp the chaotic monetary system by backing its legal tender with the most common circulated currency - Spanish coins. Americans then began trading with "Spanish milled dollars," later termed "dollars". Congressman Robert Morris, to whom Pollock addressed his billing records, perpetuated the use of Pollock's currency sign, and was the first government official to adopt the "s" with the two lines through it." (taken from http://www.newsunlimited.co.uk/notesandqueries)

Go Hercules - The dollar sign was actually a symbol on Spanish coins at the time. The symbol was the twin Pillars Of Hercules, with a snake entwined around them. Spanish colonists used gold and silver found in South America to press a currency known as Reales, with this symbol on them. This inspired another currency, known as the Thaler, which found it's way back over to America as the dollar.

Stupid E2 Trick : If you type $ in the search box on E2, you get taken back to the home page.